WATER TREATMENT
www.heatingandventilating.net Designing out stagnation
Eff ective tank management is not optional. With legionella risks and regulatory compliance in sharp focus, intelligent control of stored water is essential for safe, effi cient building operation, says Richard Braid, managing director of Cistermiser and Kerafl o
the recognised way of demonstrating compliance. Cold water storage tanks are a necessary part of
W
ater storage may be hidden away in plant rooms, but it plays a vital role in the health and effi ciency of a building.
Poorly managed cold-water storage tanks can quickly become a source of risk: stagnant water, bacterial growth, ineffi cient turnover and unnoticed temperature changes all create conditions for Legionella to thrive. For building managers, specifi ers and M&E contractors, this means water treatment should be a top priority in safeguarding occupants and maintaining operational continuity. Water management is an important issue across
a range of sectors. In healthcare, hospitals and care homes demand rigorous legionella control where vulnerable patients are at risk, making water safety essential. In education, seasonal fl uctuations in occupancy mean automated scheduling that adjusts storage volumes during holidays is critical in reducing stagnation. Commercial offi ces bring their own challenge: with hybrid working now commonplace, occupancy levels vary signifi cantly from week to week and even day to day. UK health and safety law requires building
owners and managers to control the risk of legionella in water systems. The HSE’s L8 Approved Code of Practice sets out how this should be managed, supported by the more detailed HSG274 technical guidance. Following L8 is not mandatory, however it is
many buildings’ plumbing systems, but they come with risks if not properly maintained. Stagnation and bacterial growth occur when water is left too long or moves too slowly. Temperature fl uctuations can further increase these risks – the Legionella bacteria thrives between 20-45°C so cold water should be stored below 20°C to prevent bacterial growth. Yet in many buildings, tank management still relies heavily on manual inspections, processes that are labour-intensive, prone to error and often limited in scope. In practice, this means tank temperatures can drift into the danger zone undetected. Imbalances in divided storage tanks can also be an issue; while these tanks are designed to allow for maintenance without disrupting supply, it can lead to one compartment being used more frequently than the other, allowing water to sit stagnant and increasing the risk of contamination. For healthcare estates, education facilities and commercial buildings with variable occupancy, the risks are magnifi ed. Fluctuations in demand, from school holidays to offi ce closures, can result in tanks holding more water than necessary, raising the potential for biofi lm formation and contamination. Kerafl o’s Aylesbury KB Type delayed action
fl oat valves are a reliable solution for reducing stagnation. Unlike a traditional equilibrium valve, which begins to refi ll the tank as soon as the water level drops, the KB Type introduces a controlled delay. Only once the level has fallen to the user-set point does the valve open, moving straight from fully closed to fully open. This ensures the tank fi lls at maximum fl ow, turning water over more eff ectively and avoiding the constant “dribble top-up” that can leave water sitting in a semi-stagnant state. When the water returns to its original level, the
fl oat valve closes fully, preventing the weeping or leakage associated with equilibrium valves. The result is better circulation and fresher stored water, a simple but eff ective safeguard against bacterial growth. For tanks divided into two compartments,
where imbalances can cause one side to remain unused, Kerafl o response is the KP Twin Float Valve Kit. This system uses KB Type pilot valves in each side of the tank so that whichever valve is triggered fi rst activates the main control valve. Both compartments then fi ll simultaneously, preventing one side from remaining stagnant and reducing the likelihood of biofi lm development. Mechanical solutions such as delayed action
valves are eff ective, but when combined with smart electronic control the benefi ts are multiplied. The Tanktronic system is an advanced monitoring and management solution that allows water storage to be precisely controlled. Sensors in the tank monitor both water levels and
temperature in real time, feeding data to a central control panel. The system operates with a two- stage alert: fi rst raising a warning if parameters are exceeded, then automatically overriding if no corrective action is taken. This proactive approach allows facilities managers to address issues before water conditions deteriorate. In buildings with fl uctuating occupancy, such
as universities or hotels, Tanktronic’s scheduling function can be set to adjust storage volumes during quiet periods, reducing the volume of water sitting unused. Remote access allows managers to monitor conditions and make adjustments without needing direct access to the tank. Building owners and managers have a legal duty under health and safety law to control the risk of legionella and the HSE’s L8 Approved Code of Practice, supported by HSG274 guidance, is the recognised way to demonstrate compliance. Manual checks and remedial fl ushing programmes take up staff time, often diverting resources from other maintenance priorities. Intelligent tank management automates much of this process, reducing the burden on facilities teams while ensuring a higher standard of water hygiene. Cold-water storage tanks may not attract the same attention as other building services, but their management is fundamental to occupant safety and system effi ciency. As water treatment rises up the agenda for building managers and specifi ers, intelligent solutions are setting a higher standard in risk management. By ensuring optimal turnover, preventing stagnation and delivering precise control, they provide a straightforward route to compliance while reducing cost and complexity.
24 October 2025
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